Re: [Xenomai-core] syscall restart issue with SIGINFO handlers

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
> Hi Gilles,
> 
> here is a case so far uncaught by Xenomai syscall restart code:
> 
> #include <pthread.h>
> #include <stdio.h>
> #include <signal.h>
> #include <unistd.h>
> #include <sys/mman.h>
> #include <native/task.h>
> #include <native/mutex.h>
> 
> RT_MUTEX mutex;
> pthread_t pthread;
> 
> void sighand1(int sig)
> {
> 	printf("signal 1: %d\n", sig);
> }
> 
> void sighand2(int sig, siginfo_t *si, void *context)
> {
> 	printf("signal 2: %d\n", sig);
> }
> 
> void thread(void *arg)
> {
> 	int res1, res2;
> 
> 	pthread = pthread_self();
> 
> 	res1 = rt_mutex_acquire(&mutex, TM_INFINITE);
> 
> 	res2 = rt_mutex_release(&mutex);
> 
> 	printf("res = %d / %d\n", res1, res2);
> }
> 
> int main()
> {
> 	struct sigaction sa;
> 	RT_TASK task_main, task;
> 
> 	mlockall(MCL_CURRENT|MCL_FUTURE);
> 
> 	signal(SIGUSR1, sighand1);
> 
> 	sigemptyset(&sa.sa_mask);
> 	sa.sa_sigaction = sighand2;
> 	sa.sa_flags = SA_SIGINFO;
> 	sigaction(SIGUSR2, &sa, NULL);
> 
> 	rt_task_shadow(&task_main, "main", 1, 0);
> 
> 	rt_mutex_create(&mutex, "mutex");
> 	rt_mutex_acquire(&mutex, TM_INFINITE);
> 
> 	rt_task_spawn(&task, "thread", 0, 2, 0, thread, 0);
> 
> 	sleep(1);
> 	pthread_kill(pthread, SIGUSR1);
> 
> 	sleep(1);
> 	pthread_kill(pthread, SIGUSR2);
> 
> 	rt_mutex_release(&mutex);
> 
> 	rt_task_delete(&task);
> 
> 	return 0;
> }
> 
> 
> Sending SIGUSR2 will make the blocked thread see -EINTR as result of its
> rt_mutex acquire. Some different path must be taken by libc when
> delivering SA_SIGINFO signals and returning to the application. Can you
> confirm this?

If you want syscalls to be automatically restarted, you should pass the
SA_RESTART flag to sigaction. It is unrelated to SA_SIGINFO unless I
missed something.

-- 
					    Gilles.